This invention relates to a catalyst material, and its method of making and manufacture, useful for a diversity of chemical production processes as well as various emission control processes. More specifically, it relates to a catalyst composition, preferably comprising a metal oxide felt substrate, with one or more functional surface active constituents integrated on and/or in the substrate surface, which can be used in the removal of sulfur from hot gases as well as acting to trap solid particulates and metals within these hot gases.
IGCC (Integrated Gasification Combined Cycle) is a type of power plant that gasifies coal into synthetic gas (syngas) to power a gas turbine. In these plants there is a need to remove a variety of impurities, including sulfur compounds from the syngas. After the impurities are removed, the heat from the gas turbine exhaust generates steam to run a steam turbine.
The integration of the combination of coal gasification, gas turbines, and steam turbines into electric power plants is new and presents engineering challenges. IGCC plants are to be contrasted to traditional coal powered power plants where the coal is pulverized and then burnt to produce steam to drive a turbine. Gasification is the thermal conversion of carbon-based materials at 760° to 1538° C. (1400° to 2800° F.), with a limited supply of pure oxygen, to a synthetic gas, also known as a syngas as compared to combustion which occurs when there is a surplus of oxygen.
Syngas typically contains about 35% H2, 45% CO, 5% H2O, 15% CO2 with a small amount of methane, as well as impurities such as solid particulates, sulfur compounds (mainly H2S and COS) and nitrogen compounds as well as smaller quantities of other impurities. The syngas can be used as a fuel to generate power, or to make chemicals and fuels. The heating value is 264 kjoules (250 Btu/scf).
The hot exhaust gas from the gasification reaction is sent to a steam turbine which generates steam to produce electricity. In addition, the syngas is sent to a combustion turbine which turns a generator. The combined cycle is the combination of a simple cycle combustion turbine generator plus a steam turbine generator. The sulfur compounds need to be removed from the hot exhaust gas.
IGCC technology produces air emissions that are already considerably lower than required by current U.S. Clean Air standards. Significant reductions in sulfur dioxide (SO2), nitrogen oxides (NOX) and carbon monoxide (CO) are possible through use of IGCC plants, making them more advantageous than conventional coal power plants. Carbon dioxide (CO2), which is considered a major source of global warming, can be captured more economically with IGCC than with conventional technologies. The CO2 could be sequestered or sold in part as a by-product. Overall efficiency is approximately 40 to 45% of the energy value of coal converted to electricity. In comparison, conventional coal plants are approximately 30 to 35% efficient. Water requirements are typically about 50% less for IGCC applications than for conventional coal generation. Marketable by-products from the IGCC process can be sold, such as sulfur. However, IGCC facilities are more expensive to build than conventional coal plants. Only recently have suppliers begun to emerge that can offer comprehensive, integrated designs with packaged systems and compatible equipment. Due to the industry's limited experience with the technology, truly accurate cost estimates for construction and operating costs are not yet available for use in planning future facilities.
IGCC technology requires more frequent maintenance with longer maintenance outages, requiring that power be purchased from other resources when the IGCC plant is unavailable. Neither of the U.S.-based IGCC projects has used Powder River Basin, or western, coal, which is the type used most frequently in the Midwest. The industry is encouraging suppliers to offer performance contracts for next-generation IGCC plants, but for now, the risk of reduced reliability and availability add significant cost to the project's financing.
Only a few IGCC projects have been built world-wide despite the potential benefits of the technology. Among the improvements that are sought are methods of cleaning up the hot coal derived gases produced in an IGCC project. In prior art systems, wet scrubbing techniques have been used to clean up the gases. Unfortunately, these systems require first cooling of the gas and then a subsequent reheating step.
The clean-up of hot coal-derived gases originating from an Integrated Gasification Combined Cycle (IGCC) avoids the sensible heat loss due to the cooling and subsequent reheating associated with the wet scrubbing techniques using either chemical or physical solvents. If the fuel gas is cleaned with the conventional cold gas cleanup, the penalties in both thermal and overall process efficiencies will be larger for air-blown gasifiers compared to O2-blown gasifiers, because the former produces over twice the volume of fuel gas produced by the latter. But nevertheless, both air- and O2-blown gasifiers would benefit from the successful development of hot-gas cleanup techniques. Ideally, the clean-up is done at the highest inlet temperature at which the gas turbine fuel control and delivery systems can de be designed at. Hot gas cleanup may also avoid much of the operational complexity, space requirements, and capital costs associated with cool down/reheating systems or heat exchange systems. Other drivers for hot gas clean-up in IGCCs include avoiding the production of sour water (produced if the fuel gas is cooled below the dew point of water) and consequently the sour water treating, avoiding the production of “black-mud” (mixture of water-char ash) produced in water quenching or water scrubbing of particulates from the fuel gas. Also, if the particulates are removed dry via dry filtration systems, they could be recycled to the gasifier to improve fuel utilization and process efficiency.
Coal-derived fuel gases used for power generation or cogeneration have to be substantially cleaned before being either burned in a gas turbine or used for chemical synthesis, e.g., methanol, ammonia, urea production, Fischer-Tropsch synthesis. Cleanup techniques require removal of solid particulates, sulfur-containing gases, i.e., H2S and COS and all trace contaminants resulting from the gasification of coal, i.e., NH3, HCN, alkali metals, metal carbonyls, Hg, As, and Se. The successful development of hot-gas cleanup techniques depends on the ability to remove all of the above at equally high temperatures.